1. Field of the Invention
The invention is directed to the field of subsurface drilling with the use of high pressure fluid for installing, below ground, various utility items such as electrical cable, conduit, water pipes, sewer pipes and the like.
2. Description of the Prior Art
An excellent device for providing underground bore holes is disclosed and claimed in U.S. Pat. No. 4,957,173 issued Sept. 18, 1990 by Frank R. Kinnan and entitled "METHOD AND APPARATUS FOR SUBSOIL DRILLING" and assigned to the assignee of the instant invention.
As is shown in FIGS. 1 and 2 of the instant application, which are FIGS. 2 and 3 of the above-cited patent, a drilling and steering assembly 20 permits linear boring as long as the pressure of the viscous drilling fluid supplied from the trailing pipe string 18 is at or about a first predetermined level. As soon as that level is exceeded, the excess pressure acts upon a piston 55 coupled to a push rod 50 to deflect or bend steering mechanism 40 from a position aligned with its longitudinal axis as shown in FIG. to a position displaced from such axis as shown in FIG. 2. Once the change in direction of the pipe string has been accomplished, fluid pressure is reduced and the steering mechanism is allowed to return to its aligned position and boring is recommenced.
In order that maximum flexibility of steering mechanism 40 is achieved, a section 44 of tube 41 must be removed which naturally weakens the tube 41. The flexure of steering mechanism 40 for long periods of time as where a wide or long curved bore is required strains the tube 41 and can result in its premature failure.